1. Field of the Invention
The present invention relates to systems and methods for translating video formats from a first interlaced format to a second de-interlaced format. More particularly, the present invention relates to de-interlacing image fields from an interlaced video format to provide non-interlaced frames in the presence of multiple interlacing modes including the “3:2 pulldown” mode.
2. Description of Related Art
Typical television video formats include interlaced fields of image data, so that a single image frame is constructed by a combination of interlaced fields. For example, interlaced fields for a particular image frame include the first field that stores even-numbered lines in the image frame, and a second field that stores odd-numbered lines in the image frame. The NTSC standard television format includes frames provided as two interlaced fields, which are provided at a frequency of 60 fields per second (30 frames per second).
New digital display formats are often designed for non-interlaced frames. In order to convert a stream of interlaced fields into a stream of non-interlaced frames, the complementary even and odd fields are matched and combined to produce a single frame. For video streams that are encoded according to the standard interlacing scheme, the deinterlacing process is straightforward. However, a significant amount of video programming was initially recorded on film using a standard 24 frames per second. A standard of encoding such film known as “3:2 pulldown” developed based on the recognition that if you provided 60 fields per second, 5 fields are required for every two frames incoming at 24 frames per second. Thus, the encoding process would provide 3 fields from a first frame followed by two fields from a second frame, followed by three fields from a next frame, two from the next, and so on, in a 3:2 pulldown mode. This encoding technique is shown in FIG. 1, where four incoming frames A, B, C and D are encoded as ten outgoing fields AE, AO, AE, BO, BE, CO, CE, CO, DE, DO.
When de-interlacing video encoded using the 3:2 pulldown mode, unless special logic is applied, fields are paired erroneously. As can be seen in FIG. 1, if every current field is paired as would be appropriate for a standard interlace, to provide an output non-interlaced frame, errors occur. Thus, in FIG. 1, the fourth non-interlaced frame would be composed of a combination of the odd field BO of frame B with the even field AE of frame A. Other erroneous pairings also occur, as can be seen from FIG. 1.
Techniques have been developed to detect the 3:2 pulldown mode in incoming streams in order to recognize the interlacing pattern so that it may be corrected for during a de-interlacing process. Representative prior art systems are described in Gove et al., U.S. Pat. No. 5,390,071; Christopher et al., U.S. Pat. No. 5,689,301; and Swan, U.S. Pat. No. 6,055,018.
It is desirable to provide an apparatus and method for de-interlacing an incoming video stream, which detects the 3:2 pulldown mode quickly, accurately and in real-time which is based on simple logic that is practical for implementation in integrated circuit video controllers.